Albert Barnes Commentary Psalms 69:11

"When I made sackcloth my clothing, I became a byword unto them." — Psalms 69:11 (ASV)

I made sackcloth also my garment - I put on sackcloth. This was often done as expressive of grief and sorrow. See (Psalms 30:11), note; (Psalms 35:13), note. Compare (Isaiah 22:12); (Daniel 9:3). In the case here referred to, this was an act of religion; an expression of penitence and humiliation.

And I became a proverb to them - A jest, a subject of derision, a by-word. They ridiculed me for it. Compare (1 Kings 9:7).